Kinetic investigation of CO2 reforming of dimethyl ether in a nanosecond pulsed discharge

Abstract

The chemical kinetics of plasma-assisted CO₂ reforming of dimethyl ether (DME) was investigated through combined experimental and numerical approaches. Experiments were conducted in a flow reactor (DME/CO₂/Ar, 340 K, 30 Torr) with a nanosecond repetitively pulsed dielectric barrier discharge (DBD). Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was utilized to enable comprehensive species identification and quantification. Nine ions were detected: CH₃⁺, O⁺, Ar²⁺, CO⁺, CHO⁺, Ar⁺, CO₂⁺, CH₃OCH₂⁺, and CH₃OCH₃⁺. Key neutral intermediates and products identified based on the mass spectra and photoionization efficiency (PIE) spectra included methane (CH₄), water (H₂O), acetylene (C₂H₂), carbon dioxide (CO), ethylene (C₂H₄), formaldehyde (CH₂O), ethane (C₂H₆), methanol (CH₃OH), oxygen (O₂), ketene (CH₂CO), methyl hydroperoxide (CH₃O₂H), ethyl methyl ether (CH₃OC₂H₅), methyl formate (CH₃OCHO), and dimethoxymethane (CH₃OCH₂OCH₃). Mole fraction profiles were measured as a function of inlet CO₂ concentration (3 % to 18 %, n_DME = 3 %). The consumption of DME and formation of CH₃OCHO were promoted with the addition of CO₂, and the mole fractions of some products such as H₂O, CO, CH₃OH, and CH₃OCH₂OCH₃ exhibited a rise-and-fall pattern, while other species showed a monotonic decrease. A kinetic mechanism integrating plasma and combustion reactions was developed and validated against the experimental data, showing good predictive capability. Rate of production (ROP) analysis identified three primary DME consumption pathways: H-atom abstraction by O/H/OH radicals, dissociation induced by plasma-activated species such as electrons, Ar⁺, and Ar*, and protonation by ions. H-atom abstraction pathways were enhanced, while the dissociation channels were suppressed with increasing CO₂. Under the conditions investigated, more than 60 % of the CO₂ consumption can be attributed to the electron/Ar* induced dissociation, forming CO and O, and the O radicals can promote DME low-temperature oxidation reactions.